1. Field of the Invention
The invention is drawn to a method for the production of ketones such as 2-undecanone or 3-dodecanone from glycerides, particularly from plant oils and most particularly glycerides of decanoic acid. The invention is also drawn to metal oxide catalysts for producing the ketones in high yields.
2. Description of the Prior Art
The coupling of organic acids to produce symmetrical ketones dates to the late 19th century when Squibb published the improved synthesis of acetone in which he demonstrated continuous production of acetone from acetic acid vapors in a red-hot iron tube [E. R. Squibb, J. Am. Chem. Soc. 17 (1895) 187-201]. Prior to this, acetone was prepared by the destructive decomposition of calcium acetate. Scheme 1 shows the formation of acetone from acetic acid along with the side products of water and carbon dioxide. The high conversions and selectivity of the reaction, along with water and carbon dioxide as lone side products, makes the process environmentally benign. Only the high temperatures required for conversion can detract from this portrayal.

This reaction has been further developed to include the synthesis of 3-pentanone from propionic acid [O. Nagashima, S. Sato, R. Takahashi, T. Sodesawa, J. Mol. Catal. A: Chem. 227 (2005) 231-239], cyclopentanone from the cyclization of adipic acid [M. Renz, Eur. J. Org. Chem. 2005 (2005) 979-988], and larger ketones such as 7-tridecanone from heptanoic acid and its alkyl esters [C. A. Gaertner, J. C. Serrano-Ruiz, D. J. Braden, J. A. Dumesic, J. Catal. 266 (2009) 71-78; and M. Gliński, J. Kijeński, Appl. Catal., A Gen. 190 (2000) 87-91], as well as fatty acid methyl esters from rapeseed oil to give symmetrical ketones of up to 35 carbons in length [R. Klimkiewicz, H. Teterycz, H. Grabowska, I. Morawski, L. Syper, B. Licznerski, J. Am. Oil Chem. Soc. 78 (2001) 533-535]. Along with this long list of substrates, there is a list of catalysts employed in ketonizations that is even longer. At least sixteen metal oxides or carbonates including the alkaline earth metals Mg, Ca, and Ba on silica and carbon [S. Sugiyama, K. Sato, S. Yamasaki, K. Kawashiro, H. Hayashi, Catal. Lett. 14 (1992) 127-133], the rare-earth element Ce [Sugiyama et al., ibid; C. A. Gaertner, J. C. Serrano-Ruiz, D. J. Braden, J. A. Dumesic, Ind. Eng. Chem. Res. 49 (2010) 6027-6033; M. Glinski, J. Kijenski, A. Jakubowski, Appl. Catal., A Gen. 128 (1995) 209-217; and Y. Kamimura, S. Sato, R. Takahashi, T. Sodesawa, T. Akashi, Appl. Catal., A Gen. 252 (2003) 399-410], the actinides Th [S. S. Kistler, S. Swann, E. G. Appel, Ind. Eng. Chem. 26 (1934) 388-391] and U [J. Senderens, Bull. Soc. Chim. 5 (1909)], as well as the transition metals Fe [Kamimura et al., ibid], Cr [R. Swaminathan, J. C. Kuriacose, J. Catal. 16 (1970) 357-362], Mn [Gliński et al. (2000), ibid; M. Glinski, W. Szymanski, D. Lomot, Appl. Catal., A Gen. 281 (2005) 107-113; and A. D. Murkute, J. E. Jackson, D. J. Miller, J. Catal. 278 (2011) 189-199], V [R. Pestman, R. M. Koster, A. van Duijne, J. A. Z. Pieterse, V. Ponec, J. Catal. 168 (1997) 265-272], Ti [Pestman et al. ibid; and K. Parida, H. K. Mishra, J. Mol. Catal. A: Chem. 139 (1999) 73-80], Zr [Parida et al., ibid; and K. Okumura, Y. Iwasawa, J. Catal. 164 (1996) 440-448], and Ni, Co, and Cu as composite oxides [Nagashima et al., ibid].
Despite the large number of substrates and catalysts used to study the ketonization reaction, mechanistic details remain elusive and it is likely that different mechanisms occur with different catalysts. The defining characteristic which may drive the different mechanisms is the presence of an abstractable α-proton. For example, the cyclization of adipic acid in the presence of BaO or KF has been suggested to occur through a rapid deprotonation of one acid group followed in turn by decarboxylation to give a carbanion which cyclizes to form the enolate anion. This then loses the hydroxide group, which combines with the acid proton to form water, and cyclopentanone [L. Rand, W. Wagner, P. O. Warner, L. R. Kovac, J. Org. Chem. 27 (1962) 1034-1035]. This reaction also occurs, albeit at lower yields, with 2,2,5,5-tetramethyladipic acid, which lacks the α-proton. Such a mechanism is consistent with experiments based on the decomposition of acid salts but doesn't describe reactions over heterogeneous catalysts, which are becoming more common. In the ketonization of acetic acid with these catalysts, it is proposed that surface reactions occur to deprotonate or dehydrate the acid to the acetate ion and ketene, respectively. Depending on the lattice energy of the catalyst, two routes can then be followed. Low energy salts such as BaO and MgO form metal acetates which decompose to form acetone. On high lattice energy solids, the surface-bound acetate reacts with an adjacent intermediate and an adsorbed proton to give acetone. Formation of the proposed intermediate lying planar on the catalyst surface requires the abstractable α-proton [Pestman et al., ibid].
Acid esters, alcohols, and aldehydes have also been subject to ketonization studies but mechanistic information is more limited with these substrates. The reaction of n-propanol over CeO2—Fe2O3 composite catalysts at 450° C. yields 3-pentanone in 61-75% but also produces hydrocarbons and CO, indicative of pyrolysis occurring at this high temperature [Kamimura et al., ibid]. The reaction of propanal over these same catalysts at 400° C. gave 3-pentanone in yields of up to 82%. Ketonization of methyl esters of fatty acids over a Sn—Ce—Rh—O catalyst gave the expected large symmetrical ketones at about 45% yield along with about 5% methylketones and 15% hydrocarbons [Klimkiewicz et al., ibid]. Here the low volatility of the substrates and products likely led to pyrolysis and low ketone yields.